Is it important to have your URL somewhere in your Meta Title? example..... Used Cars, New Cars, Buy a Car, Sell a Car, Car Dealers - AutoTrader.com
Is important to have your keywords in several places. IMO the importance order is 1.- Title 2.- Domain name 3.- Description 4.- URL (not domain name).
There is no such thing as a META title. There IS however the TITLE element, which is comprised of an opening <title> tag and an closing </title> tag. As for your example, if you want to use the domain name in the page title, I'd go with something else, other than stuffing keywords in there like a hot-dog eating champion stuffs his face full of hot dogs at a competition. Something like this: Buy or Sell New or Used Cars at AutoTrader.com (Yes, the example stinks, but it gets the point across.) And then save the "Car Dealer" search term for the page's META description tag.